DIYbanter - View Single Post - Compact Florescents burn out at the same time

In article ,
wrote:

On Fri, 29 Jul 2005 01:12:24 +0000 (UTC), (Don
Klipstein) wrote:

I snip

My biggest gripe with GE now is they are outsourcing the F8T5 (not an
actual CFL but a smaller one of the "standard" fluorescents to China and
the label only claims 5,000 hours life. The F8T5 used to be claimed to
last 7500 hours. The 5,000 hour version costs no less than these ever did.

- Don Klipstein )

And what does that 5000 or 7500 hours really mean? No one really
times them.

The "Big Three" makers actualy test their fluorescent lamps in aging
tests, turning them off and restarting them every 3 hours. At least they
did and do this for ones made in their own plants.

However, lets just make a rough estimate. I would guess
that I average 30 minutes per day of lights in the bathroom. That
figure is probably a little high for actual usage, but I do
occasionally forget to shut the light off. So, 1/2 hour per day times
365 days in a year would be approximately 183 hours. So, lets just
round this off to 200 hours, since they were left on overnight a
couple times. I installed the bulbs about 1 1/2 years ago. (2 years
at most). That means I got at most 400 hours of usage out of these GE
CFL bulbs which are rated at 5000 hours. At this rate, I did not even
get 10% of their rated life.

At my rate of usage, they SHOULD have lasted 12.5 years.

These bulbs were NOT enclosed in glass, and the base was DOWN.

I don't think I'd complain if I got even half the rated life, but I
didn't even get 10%.

That 5000 hour rating means nothing as far as I am concerned.
And how is that measured? Is it supposed to be continuous use, or
ON/OFF total use?

Usually the rating is for total "on" time with an average of 3 hours
"on" time per start.

I heard that turning an indecesant bulb on and off shortens their life.

Most incandescents do not lose much life from this, despite
incandescents usually burning out during a cold start, and despite cold
starts even visibly shaking the filament or causing the filament to
produce a "ping" sound audible at close range in a quiet room. (Some
incandescents do suffer significant filament fatigue from cold starts, but
most don't.)
What happens is that an aging filament becomes unable to survive a cold
start a little before it becomes unable to survive continuous operation.

Filament failure from a cold start is usually from a filament with a
thin spot from uneven evaporation experiencing a temperature overshoot of
the thin spot. The thin spot melts during a cold start. However, these
thin spots will only survive continuous operation for a limited amount of
time if they are already unable to survive a cold start, since once they
get that bad they are worsening at a rate that accelerates worse than
exponentially.

Is that also true with CFL bulbs?

Yes, that is true, and much more true than with incandescents. The
filaments in fluorescents do suffer actual extra wear from starting.

Some are worse than others for use in bathrooms used mainly for short
trips, although I doubt any are really good if they average only a couple
minutes runtime per start.

Worse ones for this start in these ways:

1. Blink a few times before staying on.
2. Start truly instantly.
3. Start truly instantly, although with a minor sudden jump of brightness
1/4-1/2 second later.

Better ones start in these ways:

1. Delay of a fraction of a second to a second before turning on, and
then it's on without blinking.

2. The ends glow first and then the whole thing is on, without blinking.

3. The lamp fades on in a smooth, steady but rapid process taking a
fraction of a second to maybe as long as a second.

====================

I have seen in some commercial buildings restrooms with fluorescent
lights controlled by occupancy sensors. Here this makes sense since a
4-foot fluorescent only costs about a dollar when purchased several cases
at a time, and electricity savings per bulb are greater than with lower
wattages.

- Don Klipstein )